1. Technical Field
The present invention relates to a multilayer ceramic (MLC) package and, more particularly, to a multilayer ceramic package with a high frequency connector which simulates a conventional coaxial connector.
2. Description of the Prior Art
Multilayer ceramic packages have become popular design choices for a variety of devices, including integrated circuits, microwave circuits, and optoelectronic devices. Multilayer ceramic packages are usually formed of a material including alumina which can be sintered at the end of the packaging process to form a hermetic package. The use of a multilayer ceramic package to house a lightwave transmitting device is discussed in copending application Ser. No. 008,051, filed Jan. 15, 1987 and assigned to the assignee of the present application. The package disclosed in the copending application advantageously utilizes the ceramic material forming the package wall to form a stripline interconnection between an external signal source and the laser diode housed within the package. The utilization of such a microwave connection provides a vast improvement over the prior art interconnection which included conductive strips inserted through the package wall.
Stripline connectors, however, do have limitations which become apparent at very high frequency (&gt;4 GHz) applications. A stripline can be thought of as a coaxial connector, with the outer ground shielding layer cut and laid out flat to form a single ground plane. The remainder of the stripline structure consists of a dielectric layer covering the ground layer, and a signal path disposed over the dielectric. With this structure, there exists some signal loss, since a portion of the electric field emanating from the signal conductor will not be captured by the ground place. Additionally, this type of structure is susceptible to parasitic disturbances and cannot fully insulate the signal path from any other signals in the vicinity.
A true coaxial connector consists of a signal conductor completely surrounded by an insulating dielectric and the dielectric completely surrounded by the ground conductor. With this arrangement, signal loss is minimized, since all of the electric field emanating from the signal conductor remains confined in the dielectric. Additionally, a coaxial connector will electrically insulate the central signal path from any other signals in the vicinity.
One arrangement in the prior art which utilizes a coaxial conductor as a connector with a high frequency optical receiver is disclosed in U.S. Pat. No. 4,309,717 issued to R. E. Cardinal on Jan. 5, 1982. The Cardinal package, however, utilizes a coaxial connector with a metal package. In order to attach such a connector to a multilayer ceramic package, both the outside and inside walls of the package must be metallized so that the connector can be soldered to the package. This is a difficult task to perform, and as a result, this type of connector is not normally utilized with a MLC package.
Therefore, a need remains in the prior art for some means of including a coaxial-quality high frequency connector with a multilayer ceramic package.